The present invention relates to an improved getter assembly which is able to avoid deformations due to unequal thermal expansion with consequent internal strains.
It is known that the getter assemblies are widely used in tubes for the representation of visual images, such as cathode ray tubes and kinescopes. In practical use the getter assembly is heated to a high temperature, usually by means of induction at high frequency, such as to cause evaporation of the gettering material contained within the getter assembly. This latter can be located within the cathode ray tube in the so called "antenna" position or attached to the anode bottom, but, whatever its position it is usually held by means of an integral support of a support in closed contact with it such as to maintain the getter holder as far as possible from the glass wall of the cathode ray tube in order to avoid that the high temperatures reached during heating of the getter asssembly can damage or even provoke rupture of the glass.
One of the disadvantages that may occur during heating of the getter is that the getter material container, usually of an annular or circular form, can become deformed as a consequence of the unequal thermal stresses due to the close relationship between the above said mount which influences and restrains free expansion.
Mounting designs for use in getter assemblies are known: see for example detail No. 26 in FIG. 2A, 2B and 2C of U.S. Pat. No. 4,323,818. Unfortunately, as it is shown in the above figures, the antenna mount is in contact with the lower wall of the getter material holder and is welded to it at points relatively close to the outside walls.
This fact leads to at least two disadvantages:
(1) The support acts as a thermal sponge and leads to unequal heating of the getter material during evaporation and therefore to an uneven expansion and to a consequent breakage with the release of loose particles;
(2) The getter material container undergoes distortions in consequence of its unequal expansion with respect to that of the support.
An attempt to overcome these difficulties has been made by fixing the support to a central position on the container but, when the diameter of the internal sidewall is decreased its becomes mechanically difficult to perform the welding and to also locate the support element which holds the getter material container from the wall of the cathode ray tube.